The objectives of this study are to compare the safety and efficacy of Antocin maintenance therapy to placebo maintenance therapy among women with preterm labor who have achieved uterine quiescence with Antocin i.v. therapy. This is a multicenter study consisting of an open-label Antocin intravenous treatment phase followed by a randomized, parallel group, double-blind, placebo-controlled, subcutaneous maintenance treatment phase. Only those subjects who achieve uterine quiescence during the initial Antocin i.v. treatment will be randomized to receive maintenance therapy. Subsequent intravenous treatments with Antocin i.v. will be given to qualified subjects. A two year infant safety follow-up is also required. To date 11 women have been enrolled into the study. Of those, 9 had delivered and 2 remained pregnant at the time of this report. Eleven follow-up visits of the infants have occurred to date.